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> Dwarf galaxy Holmberg IX in Ursa Major
Dwarf galaxy Holmberg IX in Ursa Major
author: Nasa/Esa/Hubble Heritage Team/Novapix
reference: a-gax98-00070
Image Size 300 DPI: 32 * 33 cm
This loose collection of stars is actually a dwarf irregular galaxy, called Holmberg IX. It resides just off the outer edge of M81, a large spiral galaxy in Ursa Major. This image was taken with Hubble's Advanced Camera for Surveys in early 2006. Holmberg IX is of the so-called Magellanic type of galaxy, as its size and irregularity in structure are similar to the Small Magellanic Cloud, a neighbour to our own Milky Way. It is suspected that the dwarf galaxy was created as a result of a galactic interaction between M81 and neighbouring galaxy M82. Of the more than 20,000 stars that can be resolved in this Hubble image, only about 10% are considered to be old stars with ages of billions of years. The rest are thought to be young stars with ages of only 10 and 200 million years. Simulations predict that the triplet M81, M82, and nearby NGC 3077 had a close passage 200-300 million years ago. This close encounter may have triggered the newer star formation that has occurred in Holmberg IX.
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